|Publication number||US7164898 B2|
|Application number||US 10/474,756|
|Publication date||Jan 16, 2007|
|Filing date||Apr 10, 2002|
|Priority date||Apr 12, 2001|
|Also published as||EP1403960A1, US20040127249, WO2002084784A1|
|Publication number||10474756, 474756, PCT/2002/3586, PCT/JP/2/003586, PCT/JP/2/03586, PCT/JP/2002/003586, PCT/JP/2002/03586, PCT/JP2/003586, PCT/JP2/03586, PCT/JP2002/003586, PCT/JP2002/03586, PCT/JP2002003586, PCT/JP200203586, PCT/JP2003586, PCT/JP203586, US 7164898 B2, US 7164898B2, US-B2-7164898, US7164898 B2, US7164898B2|
|Inventors||Eiji Hankui, Toshihide Kuriyama|
|Original Assignee||Nec Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (9), Referenced by (15), Classifications (13), Legal Events (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to a wireless portable device such as personal data assistant and, more particularly, to a technique for suppressing electromagnetic coupling between a radio circuit block and a digital circuit block.
Wireless portable devices such as mobile phone and personal digital assistant have become popular due to the convenient properties thereof, and the thickness and size thereof have been remarkably reduced in these years.
The wireless portable device includes an antenna block 20, a feeding block 23, a radio circuit block 21, and a digital circuit block 23, which are mounted on the printed circuit board. The antenna bock 20 transmits and receives radio waves that are used as signals upon communication with a base station etc. The feeding block 23 delivers signals to the antenna bock 20, and transmits signals supplied through the antenna block 20 to the circuit blocks. The radio circuit block 21 processes signals that are transmitted or received through the antenna block 20. The digital circuit block 22 processes digital signals that are used for data processing. Generally, a multi-layered circuit board having multiple layers is used as the printed circuit board 10. The ground layer formed as an internal layer of the printed circuit board 10 is used as the common ground for the radio circuit block 21 and digital circuit block 22. The printed circuit board used herein includes a first layer 11 as a signaling layer, a second layer 12 as the ground layer, a third layer 13 as a power source layer, and a fourth layer 14 as another signaling layer, which are disposed in this order as viewed from the first layer 11 mounting thereon components. It is to be noted that only some of circuit patterns 24 are depicted on the third and fourth layers for simplification purpose (
In the wireless portable device as described above, if there are a plurality of transmission channels provided in the same circuit board, and the distance between adjacent transmission channels is short, interaction therebetween may be generated to cause an electromagnetic coupling. An example of the methods which can solve such a problem is described in Patent Publication JP-A-58-092101. In this method, metallized through-halls are provided between the transmission lines, which should be isolated from one another, for connecting together the upper ground conductor and the lower ground conductor, whereby electric isolation is attempted between adjacent transmission lines.
In Patent Publication JP-A-10-75108, a dielectric waveguide-tube transmission line is described which is formed by the area encircled by two arrayed via-hall groups which electrically connect together the conductor layers. This technique features a subordinary conductor layer formed parallel to the conductor layers and electrically connected to the via-holes. It is attempted to improve the transmission characteristic therein by introducing such a subordinary conductor layer. Similar conductor via-halls are used in Patent Publication JP-A-9-46008. This publication describes the technique wherein the length of a stub located on the periphery of the ground pattern is made to be less than ¼ of the wavelength of the high-frequency signal transmitted through the signal transmission line. The term “stub” as used herein means an edge that is not electrically connected to the ground pattern directly. By adopting such a configuration, a high-frequency-wave wiring board can be obtained having a reduced influence on the high-frequency signals transmitted through the signal lines.
It is to be noted that a structure such as shown in
In general, the frequencies of the signals to be handled are different between the radio circuit block and the digital circuit block. For example, the radio circuit block handles transmitted/received signals having frequencies around 1 GHz (may be around 2 GHz instead, depending on the device). On the other hand, the digital circuit block handles a clock signal having a fundamental wave of around 10 GHz, which generates higher-harmonic frequencies equal to the integral multiples of the frequency of the fundamental wave. Thus, the ground layer common to both the circuit blocks receives thereon a mixture of the transmitted/received signals of around 1 GHz (or around 2 GHz) generated from the radio circuit block and the fundamental-wave and the higher-harmonic-wave signals generated from the digital circuit block. As a result, there is a tendency that the radio circuit block and the digital circuit block are susceptible to the influence by the electromagnetic coupling due to the signals of each other.
For example, it is probable that the higher-harmonic-wave current generated in the digital circuit block and transferred through the ground layer enters a device, such as the IC, in the radio circuit block. On the other hand, it is also probable that the high-frequency current (radio-frequency-wave current) around 1 GHz generated in the radio circuit block enters the digital circuit block. In the wireless portable device having reduced size and thickness, it is general that the radio circuit blocks and the digital circuit blocks are mixed on a single circuit board in a closed relationship therebetween. Thus, the electromagnetic coupling generated between the radio circuit block and the digital circuit block tends to become more critical. It has been desired to effectively suppress the electromagnetic coupling between the radio circuit block and the digital circuit block for assuring a reliable quality in such a wireless portable device. In the above conventional techniques, there is no teaching to effectively solve the problem while noting the electromagnetic coupling of the signals having different frequencies between the radio circuit block and the digital circuit block.
The present invention provides a wireless portable device that can suppress the electromagnetic coupling between the radio circuit block and the digital circuit block, by applying the technique shown in
In the wireless portable device of the present invention, a current restriction structure is provided for suppressing such an electromagnetic coupling. The current restriction structure is comprised of a first metallic plane, a second metallic plane and an equivalent metallic plane implemented by a via-hole array. The first metallic plane is disposed as an overlying layer parallel to the printed circuit board mounting thereon the radio circuit block and the digital circuit block. The second metallic plate is disposed as an underlying layer parallel to the printed circuit board. The equivalent metallic plane implemented by the via-hole array is formed by arranging via-holes on a straight line at a narrow pitch on the above first and second metallic planes. Such an equivalent metallic plane implemented by the via-hole array is disposed at the position apart from both the ends of each of the first and second metallic planes by a distance equal to ¼ of the wavelength of the subject current to be restricted. Such an equivalent metallic plane acts as a short-circuiting plate for electrically connecting together the first and second metallic planes and the ground layer on the printed circuit board. In addition, equivalent metallic planes are also disposed on both the lateral sides of the first and second metallic planes (although a configuration without them is also possible). Using such a configuration, only the upper and lower metallic planes are connected together without connecting the ground layer thereto. By using the above configurations, a rectangular cylindrical metallic tube is formed which equivalently encloses therein the ground layer. The subject current to be restricted is a radio-frequency current generated from the radio circuit block or a higher-harmonic-wave current generated from the digital circuit block, or includes both the currents. The rectangular cylindrical metallic tube may have a structure suited to the current to be restricted. More concretely, the configuration my be such that a single rectangular cylindrical metallic tube is provided, or such that two rectangular metallic plates are provided back to back with the short-circuiting plate being common thereto.
As an example of applications of the current restriction structure, it is possible to configure the first and second metallic planes and the equivalent metallic plane to form a □-shape, wherein the □-shape encircles therein the digital circuit block or the radio circuit block at the center thereof. In such a case, the basic principle is also similar to that as described above. For strengthening the connection or enhancing the function as the short-circuiting plate, a part or whole of the via-hole array may be arranged in a plurality of rows. Further, the first and second metallic planes may be respectively included in the signaling layer or the power source layer. The effects of the present invention can be obtained so long as the overlying and underlying metallic planes are provided to sandwich therebetween the printed circuit board. Further, even in the case wherein the printed circuit board is received in a metallic package casing, the current restriction structure of the present invention can be applied thereto while assuming that the package casing is the ground layer of the printed circuit board.
Embodiments of the wireless portable device according to the present invention will be described in detail with reference to the drawings. Each printed circuit board shown herein is a four-layer circuit board (first layer/signaling layer; second layer/ground layer; third layer/power source layer; and fourth layer/signaling layer), similarly to the structure of the conventional device. The space between adjacent layers of the circuit board is filled with a dielectric material such as a glass epoxy material etc., although not specifically depicted. The via-hole used herein is such that a conductive layer is formed around an air hole. The via-hole penetrating a metallic pattern is thereby connected to the metallic pattern. It is to be noted that aligned positions of the layers at which a via-hole penetrates are provided with holes to be used for the via-holes.
The ground layer 4 is configured to have a width somewhat smaller than the width of a portion of the metallic planes sandwiched between the via-hole arrays. Accordingly, the width of this portion of the metallic planes is somewhat larger than the width of the ground layer. The overlying metallic plane 2 and the underlying metallic plane 3 have the same dimensions, wherein the length thereof as viewed in the direction connecting together the radio circuit block and the digital circuit block is L (=Lr+Ld), and the width in the direction normal thereto is same as the width of the circuit board. Each of these metallic planes is obtained by combining two metallic strips (a metallic strip having a length of Lr and located on the side of radio circuit block, and another metallic strip having a length of Ld and located on the side of the digital circuit block) at the via-hole array as the boundary therebetween, as will be described later.
The lengths of Lr and LdB of the metallic strips are set at ¼ of the wavelengths of the subject current to be restricted. For example, assuming that fr is the frequency of the radio-frequency current (corresponding to a wavelength of λr) to be restricted from entering the digital circuit block out of the radio circuit block, and that fd is the frequency of the higher-harmonic-wave current (corresponding to a wavelength of λd) to be restricted from entering the radio circuit block out of the digital circuit block, the Lr and Ld are expressed by the following equations:
Lr=λr/4=(c 0 /fr)/4 (1), and
Ld=λd/4=(c 0 /fd)/4 (2),
wherein co is the velocity of light (3×108 m/s).
As depicted, the via-holes penetrate from the first layer to the third layer, wherein the via-holes disposed Lr apart from one end of the metallic planes (disposed Ld apart from the other end) electrically connect together the overlying and underlying metallic planes and the ground layer. In addition, the via-holes disposed on both lateral sides of the metallic planes electrically connect together the overlying and underlying metallic planes (without connecting to the ground layer). That the via-holes disposed on both lateral sides of the metallic plane do not connect the ground layer results from the fact that the width of the metallic planes is larger than the ground width at the position and thus the via-holes penetrate the printed circuit board without penetrating the ground layer.
In the present invention, the spacing between the adjacent via-holes is significantly shorter than the wavelength to be considered, whereby the via-holes are disposed at a narrow pitch or at a high density. This allows the via-hole array to be construed as an equivalent metallic plate. In consideration of this fact, the current restriction structure 1 can be equivalently expressed by the structure of a rectangular cylindrical metallic tube shown in
As understood from
The first current restriction unit 1 a has a configuration wherein the distal end thereof as viewed from the radio circuit block is short-circuited. The metallic strips formed as the overlying, underlying and side layers for the ground layer have a length (Lr) equal to ¼ of the wavelength, λr, of the subject radio-frequency current in the direction connecting together the radio circuit block and the digital circuit block. In this manner, the current restriction unit has a configuration wherein a transmission line (having a shortcircuited distal end) is formed to enclose therein a ground layer, and the transmission line has a length of λr/4. Thus, the input impedance against the radio circuit block is higher at the position of the open plane of the first current restriction unit 1 a. The effect of this higher impedance is that the radio-frequency current generated from the radio circuit block and transferring through the ground layer is prevented from flowing toward the digital circuit block, whereby the electromagnetic coupling can be suppressed. On the other hand, the second current restriction unit 1 b has a configuration wherein the distal end thereof as viewed from the digital circuit block is shortcircuited. The metallic strips formed as the overlying, underlying and side layers for the ground layer have a length (Ld) equal to ¼ of the wavelength, λd, of the subject higher-harmonic-wave current in the direction connecting together the radio circuit block and the digital circuit block. Thus, also in this case, the input impedance against the digital circuit block is higher at the position of the open plane of the second current restriction unit 1 b. The effect of this higher impedance is that the higher-harmonic-wave current generated from the digital circuit block and transferring through the ground layer is prevented from flowing toward the radio circuit block whereby the electromagnetic coupling can be suppressed.
As described above, in the wireless portable device of the present embodiment, the effect of the current restriction structure is that the higher-harmonic-wave current is restricted from entering the radio circuit block out of the digital circuit block, and the radio-frequency current is restricted from entering the digital circuit block out of the radio circuit block. This suppresses the electromagnetic coupling between the radio circuit block and the digital circuit block, thereby assuring a more excellent quality for the wireless portable device.
In the present embodiment, the principle is same as that of the first embodiment, although there is no metallic strip disposed on both the lateral sides (it is not a “tube” in a strict meaning; however, may constitute a rectangular cylindrical metallic tube in principle). More specifically, due to a higher input impedances at the respective open planes of the first and second current restriction units having lengths of λr/4 and λd/4, respectively, measured from the short-circuiting plate 6, the current generated from one of the circuit blocks is prevented from flowing to the other of the circuit blocks. Thus, the electromagnetic coupling can be suppressed similarly to the first embodiment.
In the first and second embodiments, there are shown wireless portable devices capable of suppressing the electromagnetic coupling between the radio circuit block and the digital circuit block.
Similarly, as a configuration of a fourth embodiment of the present invention, the wireless portable device may mount thereon a current restriction structure for restricting the radio-frequency current from entering the digital circuit block out of the radio circuit block (
In the embodiments described heretofore, the via-hole array described therein has a single row. Referring to
In the present embodiment, the □-shaped metallic planes (overlying metallic plane 32 and underlying metallic plane 33) are disposed parallel to the overlying and underlying layers (first layer and third layer) to sandwich therebetween the ground layer. Each of the metallic planes is configured to a pattern having therein an opening, which is somewhat larger than the size of the periphery of the digital circuit block, and having a widthwise length of Lr+Ld as in the cases of the above embodiments. The via-hole array is disposed apart from the inner edge of the metallic plane by a desired distance (Ld) to form a □-shape, wherein individual via-holes penetrate from the first layer to the third layer. The overlying and underlying metallic planes and the ground layer are connected together at the locations at which the via-holes reside, and the spacing of adjacent via-holes is considerably smaller than the wavelength to be considered and thus adapted to a narrow pitch and high density mounting. Thus, the via-hole array can be construed as a metallic plate also in this case. The □-shaped via-hole array is located at a distance of Ld apart from the inner edge of the metallic plane and at a distanced of Lr apart from the outer edge thereof, whereby these lengths are set at ¼ of the wavelengths of the subject currents to be restricted.
In the above first through fifth embodiments, the current restriction units are disposed between the circuit blocks which is may involve an electromagnetic coupling therebetween, having an effect on the current flowing into the ground layer of the printed circuit board. On the other hand, in the present embodiment, the □-shaped current restriction structure is disposed to surround the location at which the current is generated (the circuit block surrounded may be either a digital circuit block as in the present embodiment or a radio circuit block). Thus, the present embodiment has the advantage of restricting the current, which may possibly cause the electromagnetic coupling, from flowing onto the printed circuit board. It is to be noted that a printed circuit board may have eight layers or sixteen layers, for example, other than the four layers in the wireless portable device of the present invention, although the four-layer circuit boards are exemplified heretofore. In addition, although the metallic planes (2 and 3) formed to overlie and underlie the ground layer are included in the signaling layer and the power source layer (first layer and third layer), respectively, independent layers having the metallic planes may be provided separately from these layers. Or else, it is possible to employ a configuration wherein either one of the overlying and underlying metallic planes is included in the signaling layer or the power source layer.
In the embodiments to follow, modifications from the above embodiments will be exemplified. The advantages of the present invention in the modifications are also similar to those in the above embodiments. Referring to
It is to be noted that some of the package casings for the wireless portable devices may be made of a metallic material, although most of them are made of a nonmetallic material such as plastics or resin. In such a case, a current which may possibly cause the electromagnetic coupling may flow on the surface of the package casing. For suppressing the electromagnetic coupling caused by such a current, as shown in
As described above, in the wireless portable device of each embodiment of the present invention, since the current restriction structure restricts the higher-harmonic-wave current from entering the radio circuit block out of the digital circuit block, and the radio-frequency current from entering the digital circuit block out of the radio circuit block, the electromagnetic coupling between the digital circuit block and the radio circuit block can be suppressed to assure a higher quality.
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|U.S. Classification||455/311, 455/312|
|International Classification||H01Q23/00, H04B1/08, H04B1/10, H04B1/38, H01P3/18, H04B15/00, H01Q1/52|
|Cooperative Classification||H04B1/08, H04B1/3833|
|European Classification||H04B1/08, H04B1/38P2|
|Oct 10, 2003||AS||Assignment|
Owner name: NEC CORPORATION, JAPAN
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:HANKUI, EIJI;KURIYAMA, TOSHIHIDE;REEL/FRAME:015053/0059
Effective date: 20031008
|Sep 23, 2008||CC||Certificate of correction|
|Oct 14, 2008||CC||Certificate of correction|
|Jun 16, 2010||FPAY||Fee payment|
Year of fee payment: 4
|Jun 18, 2014||FPAY||Fee payment|
Year of fee payment: 8
|Sep 11, 2014||AS||Assignment|
Owner name: LENOVO INNOVATIONS LIMITED (HONG KONG), HONG KONG
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:NEC CORPORATION;REEL/FRAME:033720/0767
Effective date: 20140618